Impurity reduction in Olefin metathesis reactions

ABSTRACT

The present invention relates to the use of isomerization inhibitors in olefin metathesis reactions. The inhibitors are low molecular weight organic acids such as formic acid, acetic acid, benzoic acid, and the like.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. Ser. No. 10/155,854, filed May24, 2002, which is a continuation-in-part of U.S. Ser. No. 09/833,018,filed Apr. 10, 2001, filed as 371 of International Application No.PCT/US00/31549, filed Nov. 17, 2000, and which is a continuation of U.S.Ser. No. 09/387,486, filed Sep. 1, 1999, now U.S. Pat. No. 6,215,019.The disclosures of the aforementioned applications are incorporated byreference in their entireties.

TECHNICAL FIELD

The invention relates generally to catalytic olefin metathesisreactions, and more particularly relates to additives used in suchreactions to reduce the production of unwanted byproducts and therebyimprove the yield and purity of the desired reaction products.

BACKGROUND

To the synthetic organic or polymer chemist, simple methods for formingcarbon-carbon bonds are extremely important and valuable tools. “Olefinmetathesis,” as is understood in the art, is one such method and refersto the metal-catalyzed redistribution of carbon-carbon bonds. See Trnkaand Grubbs (2001) Acc. Chem. Res. 34:18-29. Over the past decade, olefinmetathesis has emerged as a powerful carbon-to-carbon bond-formingreaction that is widely used in organic synthesis and polymer science.This is largely due to the development of certain transition metalalkylidene complexes that have proven to be highly active metathesiscatalysts. These catalysts, developed by Robert H. Grubbs at theCalifornia Institute of Technology, are described, inter alia, in U.S.Pat. Nos. 5,312,940, 5,342,909, 5,831,108, 5,017,071, 5,969,170,6,111,121, and 6,211,391 to Grubbs et al., and in Bourissou et al.(2000) Chem. Rev. 100:39-91 Trnka and Grubbs (2001), supra. The current“Grubbs catalysts,” in which a central ruthenium atom is substitutedwith an N-heterocyclic carbene ligand, offer many advantages, includingreadily tunable steric bulk, vastly increased electron donor character,compatibility with a variety of metal species, improved thermalstability, and tolerance of a wide variety of functional groups on theolefinic reactants. See Scholl et al. (1999) Tetrahedron Lett.40:2247-2250; Scholl et al. (1999) Org. Lett. 1:953-956; Chatterjee etal. (2000) J. Am. Chem. Soc. 122:3783-3784; and Bielawski et al. (2000)Angew. Chem. Int. Ed. 39:2903-2906.

The ruthenium metathesis catalysts and derivatives thereof have firmlyestablished olefin metathesis as a versatile and reliable synthetictechnique for advanced organic synthesis, and have proven to be usefulin connection with a number of different types of metathesis reactions,including cross-metathesis (e.g., ethenolysis), ring-closing metathesis(RCM), ring-opening metathesis (ROM), ring-opening metathesispolymerization (ROMP), and acyclic diene metathesis (ADMET)polymerization. The metathesis reaction products have a variety of uses;for example, alpha olefins are useful in the preparation of poly(olefin)polymers, alpha, omega ester-functionalized olefins can be converted tothermoset polymers such as epoxy resins and polyurethanes, and the like.As with any commercially significant chemical processes, however, thereis an ongoing interest in improving the purity and yield of the reactionproduct.

In olefin metathesis, olefin isomerization is one of the side reactionsobserved that can significantly alter the product distribution anddecrease the yield of the desired product, especially with ill-definedcatalyst systems. (Ivin, K. J.; Mol, J. C. Olefin Metathesis andMetathesis Polymerization; Academic Press: San Diego, Calif., 1997; p4.) Additionally, the side products resulting from unwantedisomerization are frequently difficult to separate via standardtechniques. Well-defined ruthenium-based olefin metathesis catalysts aregenerally highly selective for olefin metathesis; however, there havebeen some reports of olefin isomerization occurring with these catalystsas well. See, e.g., Lehman et al. (2003) Inorg Chim. Acta 345:190-198;Schmidt (2004). Eur. J. Org. Chem, 1865-1880, and references citedtherein.) Recently, the Grubbs group has shown that ruthenium hydridespecies formed from decomposition of catalysts could be responsible forthe undesirable isomerization reaction. Hong et al. (2004). J. Am. Chem.Soc. 126:7414-7415. This information has allowed for the development ofadditives to block the unwanted isomerization reaction by scavengingmetal hydrides from decomposed ruthenium catalysts, which, in turn,improves reaction products yields and purities.

Paulson and Pederson, in U.S. Patent Publication No. 2003/0023123 A1,described the use of (1) low temperature reaction conditions, and (2)halogenated alkanes, halogenated aromatics, quinones, halogenatedquinones, BHT, and vitamin E as isomerization inhibitors, in order toincrease purity in metathesis reactions. There is nevertheless anongoing need for additional isomerization inhibitors that increase thepurity and yield of desired metathesis products.

SUMMARY OF THE INVENTION

The present invention describes the use of acidic isomerizationinhibitors in olefin metathesis reactions to reduce unwanted reactionproducts resulting from olefin isomerization, thereby significantlyimproving yields and greatly reducing impurities.

In one embodiment, the invention provides a method for carrying out anolefin metathesis reaction, comprising contacting at least one olefinicreactant with an olefin metathesis catalyst at a temperature in therange of −72° C. to about 20° C. in the presence of an effective amountof an isomerization inhibitor.

The invention, in a further embodiment, provides a method for carryingout an ethenolysis reaction, comprising contacting ethylene and at leastone additional olefinic reactant with an olefin metathesis catalyst at atemperature in the range of −72° C. to about 20° C. in the presence of aquinone, a substituted quinone, BHT, vitamin E, and/or an organic acidhaving the formula R¹⁰—COOH where R¹⁰ is selected from H, C₁-C₆ alkyl,C₂-C₆ alkenyl, halogenated C₁-C₆ alkyl, halogenated C₁-C₆ alkenyl,phenyl, halogenated phenyl, benzyl, and halogenated benzyl, wherein theorganic acid is present in an amount effective to inhibit olefinisomerization.

The invention, in a further embodiment, provides a method for carryingout an olefin metathesis reaction, comprising contacting an α-olefin andat least one additional olefinic reactant with an olefin metathesiscatalyst at a temperature in the range of −72° C. to about 20° C. in thepresence of a quinone, a substituted quinone, BHT, vitamin E, and/or anorganic acid having the formula R¹⁰—COOH where R¹⁰ is selected from H,C₁-C₆ alkyl, C₂-C₆ alkenyl, halogenated C₁-C₆ alkyl, halogenated C₁-C₆alkenyl, phenyl, halogenated phenyl, benzyl, and halogenated benzyl,wherein the organic acid is present in an amount effective to inhibitolefin isomerization.

Preferred organic acids are low molecular weight carboxylic acids. Alsopreferred are organic acids having a pKa in the range of about 1.5 toabout 6.5.

The invention is useful in a variety of metathesis reactions, includingintramolecular reactions such as ring-closing metathesis andcross-metathesis reactions such as ethenolysis. The invention isparticularly useful in ethenolysis processes, e.g., to convert Frenewable seed oils into alpha olefins and unsaturated acids and esters,preferably alpha, omega-unsaturated acids and esters. Alpha olefins arevaluable starting monomers in the preparation of polyolefin polymers.Alpha, omega-unsaturated acids and esters can be converted by well knownchemical techniques, e.g. transesterifications, epoxidations,hydroformylations, hydrocyanations, reductive amination, and the likeinto ester-epoxide monomers, ester-alcohol monomers, diol monomers, andester-amine monomers, any of which can be polymerized to yield usefulproducts. Poly(ester epoxides) find utility, inter alia, in themanufacturing of epoxy thermoset resins. Poly(ester alcohols), polydiols, poly(ester amines) and poly(amino alcohols) are recognized ashaving utility in the manufacturing of polyurethanes.

The techniques of this invention are useful in conjunction with a widerange of olefin metathesis catalysts, including Grubbs' bis phosphinecatalysts, Grubbs' N-heterocyclic carbene-substituted rutheniuimcatalysts, and the like, including but not limited to those that areuseful in catalyzing metathesis reactions for synthesizing methyl5-hexenoate, methyl 9-decenoate, methyl 11-dodecenoate, 5-hexenoic acid,9-decenoic acid, 11-dodecenoic acid, 1-decene, 1-hexadecene,1-octadecene, 2,5-dihydrofuran and methyl5-t-butyldimethylsilyoxy-2-pentenoate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention describes isomerization inhibitors thatsignificantly improve product yields and purity in olefin metathesisreactions. The invention may be applied to any catalytic olefinmetathesis reaction to obtain yield enhancement and impurity reduction.

J As an initial matter, “olefin metathesis,” as it is understood in theart, refers to the metal-catalyzed redistribution of carbon-carbon bondsin a reaction involving an olefin. While the invention is broadlyapplicable to almost all reactions involving olefin metathesiscatalysts, some of these catalysts are better known than others. Amongthe catalysts of interest are the neutral ruthenium or osmium metalcarbene complexes that possess metal centers that are formally in the +2oxidation state, have an electron count of 16, and arepenta-coordinated. Other catalysts of particular interest include, butare not limited to, cationic ruthenium or osmium metal carbene complexesthat possesses metal centers that are formally in the +2 oxidationstate, have an electron count of 14, and are tetra-coordinated. Examplesof such metathesis catalysts have been previously described in, forexample, U.S. Pat. Nos. 5,312,940, 5,342,909, 5,831,108, 5,017,071,5,969,170, 6,111,121, and 6,211,391 to Grubbs et al., and in Bourissouet al. (2000), Trnka and Grubbs (2001), Scholl et al. (1999) TetrahedronLett. 40:2247-2250, Scholl et al. (1999) Org. Lett. 1:953-956,Chatterjee et al. (2000), and Bielawski et al. (2000), all citedpreviously herein.

The aforementioned ruthenium and osmium carbene complexes are of thegeneral formula (1):

-   -   where n=0 to 2, M is a Group 8 transition metal such as        ruthenium or osmium, X and X′ are anionic ligands, L and L′ are        neutral electron donors, and R and R′ are specific substituents,        e.g., one may be H and the other may be a substituted silyl,        substituted, or unsubstituted hydrocarbyl group such as phenyl        or —C═C(CH₃)₂. Such complexes have been shown to be useful in        catalyzing a variety of olefin metathesis reactions, including        ethenolysis, ring opening metathesis polymerization (“ROMP”),        ring closing metathesis (“RCM”), acyclic diene metathesis        polymerization (“ADMET”), ring-opening metathesis (“ROM”), and        cross-metathesis (“CM” or “XMET”) reactions. The catalysts'        broad range of applications is due in large part to their        excellent compatibility with various functional groups and        relatively high tolerance to moisture, air, and other impurities        (Schwab et al. (1995) Angew. Chem., Int. Ed. Engl. 34:2039-2041;        Schwab et al. (1996) J. Am. Chem. Soc. 118:100-110;        Ivin (1998) J. Mol. Cat. A-Chem. 133:1-16; Grubbs et al. (1998)        Tetrahedron 54:4413-4450; and Randall et al. (1998) J. Mol. Cat.        A-Chem. 133:29-40). As has been recognized by those in the        field, however, the compounds display low thermal stability,        decomposing at relatively low temperatures. See, e.g., Jafarpour        et al. (2000) Organometallics 19(11):2055-2057.

For the most part, such metathesis catalysts have been prepared withphosphine ligands, e.g., tricyclohexylphosphine ortricyclopentylphosphine, exemplified by the well-defined,metathesis-active ruthenium alkylidene complexes (II) and (III):

-   -   wherein “Cal” is a cycloalkyl group such as cyclohexyl or        cyclopentyl. See Grubbs et al., U.S. Pat. No. 5,917,071 and        Trnka et al., supra. Replacement of one of the phosphine ligands        with a        1,3-disubstituted-4,5-dihydro-(4,5-disubstituted)-imidazole-2-ylidene,        such as 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene results in a        more active catalyst because of the more electron-rich ruthenium        metal center (Scholl et al. (1999), Tetrahedron Letter        40:2247-2200 and Scholl et al. (1999), Org. Lett. 1:953-956).        Four representative second generation catalysts are the        ruthenium complexes (IVA), (IVB), (VA) and (VB):

In the above structures, “Cal” is as defined previously, “Ph” representsphenyl, “IMes” represents 1,3-dimesityl-imidazol-2-ylidene:

and “sIMes” represents 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene:

and “N-IMes” represents 1,3-dimesityl-triazolylidene:

Other complexes formed from N-heterocyclic carbene ligands are alsoknown. These transition metal carbene complexes, particularly thosecontaining a ligand having the 4,5-dihydroimidazol-2-ylidene structuresuch as in sIMes, have been found to address a number of previouslyunsolved problems in olefin metathesis reactions, particularlycross-metathesis reactions.

All of the foregoing catalysts, and other olefin metathesis catalysts,may be used in accordance with the invention.

The prior art teaches that olefin metathesis catalysts must be heatedfor activation to initiate metathesis reactions. It has recently beenfound that this approach generally renders the metathesis catalyst,including the second generation Grubbs catalysts, too aggressive intheir activity, see U.S. Patent Publication No. 2003/0023123 A1. As inthe aforementioned patent publication, the present methods and systemsare preferably conducted at a low temperature. For the N-heterocycliccarbene catalysts, reaction temperatures that will assist in impurityreduction are in the range of about of about −72° C. to about 20° C.,more preferably in the range of about −72° C. to about 10° C., mostpreferably in the range of about −5° C. to about 10° C., and optimallyin the range of about 5° C. to about 10° C.

Unless otherwise indicated, the term “yield” refers to reaction productand the term “conversion” refers to reactants consumed in the reaction.In particular, percent conversion is calculated by determining theamount (mass or moles) of a reactant consumed as a percentage of theamount (mass or moles) of that reactant initially present beforereaction commenced. Since many metathesis reactions are equilibriumreactions that do not go to a final endpoint so as to consume allreactants but can nonetheless be driven to consume one reactant byadding an excess of another, the theoretical or calculated yield ofreaction product is dependent on the proportions of reactants, if morethan one olefin is present. Thus, for a reaction consuming equimolaramounts of two reactants, where equal molar amounts of reactants arepresent initially, the yield may be derived from the conversion ofeither of the reactants. For example, if one mole of each reactant isneeded to produce one mole of product, and 0.8 moles of each reactantwas consumed out of 1.2 moles of each initially present (either due toequilibrium, or due to stopping of the reaction), and 0.6 moles ofproduct was produced, then the percent yield is 100(0.6/0.8)=75% and thepercent conversion is 100(0.8/1.2)=66.67%. In the event one of thereactants is present in excess to drive the reaction beyond theconversion achieved with equimolar amounts of the reactants, thenconversion and yield are based on the reactant of which a greaterproportion is consumed (i.e. has lowest initial amount present). Forexample, if reactants A and B combine in equimolar amounts to form C,and there are 5.0 moles of reactant A and 2.5 moles of reactant Bpresent before reaction, then, at equilibrium, after reaction, or whenthe reaction is stopped, there are 3.0 moles of A remaining and 0.5moles of B (i.e. 2.0 moles of A were consumed) and 1.8 moles of C. Thepercent conversion of A is 100(2.0/2.5)=80%, and the percent yield of Cis 100(1.8/2.0)=90%. In a ring-opening or ring-closing reaction, inwhich A converts to B, and one mole of A produces one mole of B, thepercent conversion is 100 (moles of A consumed/moles of A present beforereaction) and the percent yield is 100 (moles of B produced/moles of Aconsumed). If no impurities are produced, the theoretical yield of 100%is achieved.

The invention provides yields that approach the theoretical yields quiteclosely. Thus, in accordance with the invention, the yield is within10%, preferably 0 to 5% of the theoretically calculated yield. Forexample, if the theoretical yield is 40% based on reactants consumed,then the actual yield is greater than 30% (within 10%), and ispreferably greater than 35% (within 5%).

The metathesis reactions are run neat (i.e. without solvent) to maximizereactor space efficiency. Using an excess of one starting material willincrease the yield of product but decrease the time throughput yield.

The isomerization inhibitors herein decrease the rates of reactions thatproduce undesirable byproducts, also known as impurities. An impurity isregarded as present in an “insignificant” amount if it is present in asmall amount and is relatively easily removed. When prior art metathesisreactions are carried out in a solvent-free environment, for example,not in a methylene chloride solution as is typically done, then there istypically the formation of a substantial amount of undesirableimpurities such as those due to double bond migration. The compoundsthat represent such impurities can undergo further metathesis reactionsto produce a compound with one carbon less and one carbon more than thedesired product. This process can repeat until an equilibrium mixture ofimpurities is obtained. According to one aspect of the invention, suchimpurities can be reduced or eliminated by adding an organic acid, aquinone, a substituted quinone (e.g., a halogenated quinone), BHT(butylated hydroxytoluene), or vitamin E as an isomerization inhibitorto the reaction. The organic acid has a pKa in the range of about 1.5 toabout 6.5, preferably in the range of about 3.0 to about 4.8, and amolecular weight less than 250 g/mole, preferably less than 175 g/mole.Preferred such acids are of the formula R¹⁰—COOH where R¹⁰ is selectedfrom H, C₁-C₆ alkyl, C₂-C₆ alkenyl, halogenated C₁-C₆ alkyl, halogenatedC₁-C₆ alkenyl, phenyl, halogenated phenyl, benzyl, and halogenatedbenzyl. Examples of such acids include, without limitation, formic acid,acetic acid, benzoic acid, acrylic acid, and dichloroacetic acid. Two ormore such organic acids can also be used in combination. Additionally,other isomerization inhibitors can be used in combination with theorganic acid(s), including antioxidants such as quinone, halogenatedquinones, compounds bearing some similarity to quinone, such as BHT(butylated hydroxytoluene), and Vitamin E. The amount of theisomerization inhibitor(s) used range from about 0.009 mole to 500 molper mole of catalyst, typically 2 mole per mole of catalyst.

In general, the metathesis catalysts of most interest include, but arenot limited to, neutral ruthenium or osmium metal carbene complexesdiscussed previously, i.e., those that possess metal centers that areformally in the +2 oxidation state, have an electron count of 16, arepenta-coordinated, and are of the general formula I, shown below. Othercatalysts of particular interest include, but are not limited to,cationic ruthenium or osmium metal carbene complexes that possessesmetal centers that are formally in the +2 oxidation state, have anelectron count of 14, are tetra-coordinated, and are of the generalformula II.

wherein:

-   -   M is ruthenium or osmium;    -   n is an integer in the range of 0 to 5 inclusive;    -   L and L¹ are each independently any neutral electron donor        ligand;    -   R, R¹, and R² are each independently hydrogen or any hydrocarbyl        or silyl moiety,

X and X¹ are each independently any anionic ligand;

-   -   Y is any non coordinating anion;    -   Z and Z¹ are each independently any linker selected from the        group nil, —O—, —S—, —NR²—, —PR²—, —P(═O)R²—, —P(OR²)—,        —P(═O)(OR²)—, —C(═O), —C(═O)O—, —OC(═O), —OC(═O)O—, —S(═O), or        —S(═O)₂—; and    -   wherein any two or more of X, X¹, L, L¹, Z, Z¹, R, R¹, and R²        may be optionally joined together to form a multidentate ligand        and wherein any one or more of X, X¹, L, L¹, Z, Z¹, R, R¹, and        R² may be optionally linked chemically to a solid or glassy        support.

In preferred embodiments of these catalysts, L and L¹ are eachindependently selected from the group consisting of phosphine,sulfonated phosphine, phosphite, phosphinite, phosphonite, arsine,stilbine, ether, amine, amide, imine, sulfoxide, carbonyl, carboxyl,isocyanide, nitrosyl, pyridine, quinoline, thioether, and nucleophilicheterocyclic carbenes of the general formula III:

wherein:

-   -   A is either carbon or nitrogen;    -   R³, R⁴, R⁵, and R⁶ are each independently hydrogen or any        hydrocarbyl moiety, except that in the case where A is nitrogen        R⁵ is nil;    -   Z² and Z³ are each independently any linker selected from the        group nil, —O—, —S—, NR²—, —PR²—, —P(═O)R²—, —P(OR²),        —P(═O)(OR²_, —C(═O), —C(═O)O—, —OC(═O), —OC(═O)O—, —S(═O), or        —S(═O)₂—, except that in the case where A is nitrogen Z³ is nil;        and Z², Z³, R⁴, and R⁵ together may optionally form a cyclic        optionally substituted with one or more moieties selected from        the group consisting of C₁-C₁₀ alkyl, C₁-C₁₀ alkoxy, aryl, and a        functional group selected from the group consisting of hydroxyl,        thiol, thioether, ketone, aldehyde, ester, ether, amine, imine,        amide, nitro, carboxylic acid, disulfide, carbonate, isocyanate,        carbodiimide, carboalkoxy, carbamate, and halogen.

In some catalysts of interest, L and L¹ are each a phosphine of theformula PR⁷R⁸R⁹, where R⁷, R⁸, and R⁹ are each independently anyhydrocarbyl moiety, particularly aryl, primary C₁-C₁₀ alkyl, secondaryalkyl or cycloalkyl. In certain other embodiments, L and L¹ are selectedfrom the group consisting of —P(cyclohexyl)₃, —P(cyclopentyl)₃,—P(isopropyl)₃, —P(butyl)₃, and —P(phenyl)₃.

In the embodiments of most interest, L is a phosphine and Ll is anucleophilic carbene of the general formula III. Preferably, L isselected from the group consisting of —P(cyclohexyl)₃, —P(cyclopentyl)₃,—P(isopropyl)₃, —P(butyl)₃, and —P(phenyl)₃ and L¹ is selected from thegroup consisting of:

wherein m is an integer in the range of 0 to 5 inclusive.

Relating to R and R¹-R⁹, examples of hydrocarbyl moieties include, butare not limited to, C₁-C₂₀ alkyl, C₃-C₂₀ cycloalkyl, C₂-C₂₀ alkenyl,C₂-C₂₀ alkynyl, aryl, heteroaryl, aralkyl, and alkaryl. Examples ofsilyl moieties include, but are not limited to, tri(hydrocarbyl)silyl,tri(hydrocarbyloxy)silyl, and mixed (hydrocarbyl)(hydrocarbyloxy)silyl.Optionally, each of the R, R¹, and R² substituent groups may besubstituted with one or more hydrocarbyl or silyl moieties, which, inturn, may each be further substituted with one or more groups selectedfrom halogen, C₁-C₅ alkyl, C₁-C₅ alkoxy, phenyl, and substituted phenyl.Moreover, any of the catalyst ligands may further include one or morefunctional groups. Examples of suitable functional groups include, butare not limited to: hydroxyl, thiol, thioether, ketone, aldehyde, ester,ether, amine, imine, amide, nitro, carboxylic acid, disulfide,carbonate, isocyanate, carbodiimide, carboalkoxy, carbamate, andhalogen. In addition, any or all of L, L¹, R, R¹ and R² may be joined toform a bridging or cyclic structure.

In embodiments of particular interest, the R substituent is hydrogen andthe R¹ substituent is selected from the group consisting of C₁-C₂₀alkyl, C₂-C₂₀ alkenyl, aryl, alkaryl, aralkyl, trialkylsilyl, andtrialkoxysilyl. In certain preferred embodiments, n equals 0, 1 or 2,and the R¹ substituent is phenyl, t-butyl, or vinyl, optionallysubstituted with one or more moieties selected from the group consistingof C₁-C₅ alkyl, C₁-C₅ alkoxy, phenyl, and a functional group. Inespecially preferred embodiments, n equals 0 or 1 and R¹ is phenyl,t-butyl, or vinyl substituted with one or more moieties selected fromthe group consisting of chloro, bromo, iodo, fluoro, —NO₂, —NMe₂,methyl, methoxy, and phenyl.

In some embodiments of interest, X and X¹ are each independentlyhydrogen, halide, or one of the following groups: C₁-C₂₀ alkyl, aryl,C₁-C₂₀ alkoxide, aryloxide, C₃-C₂₀ alkyldiketonate, aryldiketonate,C₁-C₂₀ carboxylate, arylsulfonate, C₁-C₂₀ alkylsulfonate, C₁-C₂₀alkylthiol, aryl thiol, C₁-C₂₀ alkylsulfonyl, or C₁-C₂₀ alkylsulfinyl.Optionally, X and X¹ may be substituted with one or more moietiesselected from the group consisting of C₁-C₁₀ alkyl, C₁-C₁₀ alkoxy, andaryl which in turn may each be further substituted with one or moregroups selected from halogen, C₁-C₅ alkyl, C₁-C₅ alkoxy, and phenyl. Inmore preferred embodiments, X and X¹ are halide, benzoate, C₁-C₅carboxylate, C₁-C₅ alkyl, phenoxy, C₁-C₅ alkoxy, C₁-C₅ alkylthiol, arylthiol, aryl, and C₁-C₅ alkyl sulfonate. In certain preferredembodiments, X and X¹ are each halide, CF₃CO₂, CH₃CO₂, CFH₂CO₂,(CH₃)₃CO, (CF₃)₂(CH₃)CO, (CF₃)(CH₃)₂CO, PhO, MeO, EtO, tosylate,mesylate, or trifluoromethanesulfonate. In the most preferredembodiments, X and X¹ are each chloro, bromo, or iodo. In addition, Xand X¹ together may comprise a bidentate ligand.

Y may be derived from any tetra-coordinated boron compound or anyhexa-coordinated phosphorus compound. Preferred boron compounds includeBF₄ ⁻, BPh₄ ⁻, and fluorinated derivatives of BPh₄ ⁻, but others arealso useful. Preferred phosphorous compounds include, but are notlimited to, PF₆ ⁻ and PO₄ ⁻². The non-coordinating anion may be also anyone of the following: ClO₄ ⁻, SO₄ ^(═), NO₃ ⁻, OTeF₅ ⁻, F₃CSO₃ ⁻, H₃CSO₃⁻, CF₃COO⁻, PhSO₃ ⁻, or (CH₃)C₆H₅SO₃ ⁻. Y may be also derived fromcarboranes, chloro borates, carborane anions, fullerides, aluminoxanes,and the like.

The catalyst:olefin monomer ratio in the invention is preferably betweenabout 1:5 and about 1:1,000,000. More preferably, the catalyst:olefinratio is about 1:1 to 1:200, or conforms with the literature, whichusually puts the ratio in the range between about 1:10 and about1:10,000 and, most preferably, between about 1:20 and about 1:1,000 orabout 1:20 to 1:100.

Particularly preferred metal catalysts include, but are not limited to:(PCy₃)Cl₂Ru═CHPh, (PCy₃)Cl₂Ru═CH—CH═CMe₂, (PCy₃)Cl₂Ru═C═CHCMe₃,(PCy₃)Cl₂Ru═C═CHSiMe₃, (PCy₃)(s-IMes)Cl₂Ru═CH—CH═CMe₂,(PCP₃)₂Cl₂Ru═CH—CH═CMe₂, (PCp₃)₂Cl₂Ru═C═CHPh,(PCP₃)(s-IMes)Cl₂Ru═CH—CH═CMe₂, (PPh₃)(s-IMes)Cl₂Ru═C═CHCMe₃,(PPh₃)Cl₂Ru═C═CHSiMe₃, (PPh₃)Cl₂Ru═C═CHCMe₃, (P(i-Pr)₃)Cl₂Ru═C═CHPh,(PPh₃)(s-IMes)Cl₂Ru═C═CHSiMe₃, (PBu₃)₂Cl₂Ru═C═CHPh,(PPh₃)(s-IMes)Cl₂Ru═CH—CH═CMe₂, (PCy₃)(s-IMes)Cl₂Ru═C═CHPh,(PCp₃)(s-IMes)Cl₂Ru═C═CHPh, (PBu₃)(s-IMes)Cl₂Ru═C═CHPh,(PCy₃)(s-IMes)Cl₂Ru═CHPh, (PBu₃)(s-IMes)Cl₂Ru═CH—CH═CMe₂,(PCy₃)(IMes)Cl₂Ru═CH—CH═CMe₂, (PCp₃)(IMes)Cl₂Ru═CH—CH═CMe₂,(PPh₃)(IMes)Cl₂Ru═C═CHCMe₃, (PPh₃)(IMes)Cl₂Ru═C═CHSiMe₃,(PPh₃)(IMes)Cl₂Ru═CH—CH═CMe₂, (PCy₃)(IMes)Cl₂Ru═C═CHPh,(PCp₃)(IMes)Cl₂Ru═C═CHPh, (PBu₃)(IMes)Cl₂Ru═C═CHPh,(PCy₃)(IMes)Cl₂Ru═CHPh, (PBU₃)(IMes)Cl₂Ru═CH—CH═CMe₂,(PCy₃)(IMes)Cl₂Ru═C═CHCMe₃, (PCy₃)ClRu═CHPh(o-O-Isop),(PCp₃)ClRu═CHPh(o-O-Isop), (PPh₃)ClRu═CHPh(o-O-Isop),(PBu₃)ClRu═CHPh(o-O-Isop), (s-IMes)ClRu═CHPh(o-O-Isop),(IMes)ClRu═CHPh(o-O-Isop), (N-s-IMes)ClRu═CHPh(o-O-Isop), and(N-IMes)ClRu═CHPh(oO-Isop), (s-IiPrPh)ClRu═CHPh(o-O-Isop). Where(o-O-Isop) is ortho-isopropoxyphenyl methylene and s-IiPrPh is bis1,3-(2,6-diisopropyl phenyl)4,5-dihydroimidazol-2-ylidene.

For convenience and reference herein, various examples of metathesiscatalysts are identified by their molecular weight; ruthenium (II)dichloro(3-methyl-1,2-butenylidene) bis(tricyclopentylphosphine) (716);ruthenium (11)dichloro(3-methyl-1,2-butenylidene)bis(tricyclohexylphosphine) (801);ruthenium (II) dichloro (phenylmethylene)bis(tricyclohexylphosphine)(823); ruthenium (II)[1,3-bis-(2,4,6-trimethylphenyl)-2-imidazolidinylidene)dichloro(phenylmethylene) (tricyclohexylphosphine) (848); ruthenium (II)[1,3-bis-(2,4,6-trimethylphenyl)-2-imidazolidinylidene)dichloro(o-isopropoxyphenylmethylene) (627); ruthenium (H) [bis1,3-(2,6-diisopropyl phenyl)4,5-dihydroimidazol-2-ylidene)dichloro(o-isopropoxyphenylmethylene) (712); ruthenium (II)[1,3-bis-(2,4,6-trimethylphenyl)-2-imidazolidinylidene)dichloro(phenylmethylene)(triphenylphosphine)(830), and ruthenium (II) dichloro(vinylphenylmethylene)bis(tricyclohexylphosphine) (835); ruthenium (I)dichloro(tricyclohexylphosphine)(o-isopropoxyphenylmethylene) (601), andruthenium (II)(1,3-bis-(2,4,6,-trimethylphenyl)-2-imidazolidinylidene)dichloro(phenylmethylene)(bis3-bromopyridine (884)). This molecular weight-based nomenclature will beused the examples that follow.

Examples of unsaturated fatty acid feed stocks and unsaturated fattyacid seed oils suitable for ethenolysis are, but not limited to:2-butenoic acid, 2-pentenoic acid, 2,4-hexadienoic acid, 3-hexenoicacid, 2-heptenoic acid, 2-octenoic acid, 2-noneoic acid, 4-decenoicacid, 3-dodecenoic acid, 3-tridecenoic acid, 9-tetradecenoic acid,9-hexadecenoic acid, 6-octadecenoic acid, 9-octadecenoic acid (oleicacid), 9,12-octadecadienoic acid, 9,11-octadecadienoic acid,9,12,15-octadecatrienoic acid, 5-eicosenoic acid, 9-eicosenoic acid,11-docosenoic acid, 13-docosenoic acid, 21-triacontenoic acid, and12-hydroxy-9-actadecenoic acid and like acids. The preferred unsaturatedfatty acids are 9-octadecenoic acid (oleic acid), 9,12-octadecadienoicacid (linoleic acid) and 9,11-octadecadienoic acid (conjugated linoleicacid).

The following examples merely serve to illustrate certain aspects of theinvention for ease of explanation and are not to be construed as in anyway limiting the scope of the invention as described and claimed herein.

EXPERIMENTAL

(Z)-5-tert-butyldimethylsilyloxy-2-pentenoate (Herold, P.; Mohr, P.;Tamm, C. Helv. Chim. Acta. 1983, 66, 744-754), (Z)1,4-Bis(tert-butyldimethylsilyloxy)₂-butene (Jones, K.; Storey, J. M. D.Tetrahedron, 1993, 49, 4901-4906) and 11-eicosenyl acetate (Pederson, R.L.; Fellow, I. M.; Ung, T. A.; Ishihara, H.; Hajela, S. P.; Adv. Synth.Catal. 2002, 344, No. 6+7, 728-734) were prepared according toliterature procedures. Diallyl ether was purchased from Aldrich and usedas received. Methyl oleate was purchased from Nu-Chek Prep (Elysian, MN). Meadowfoam oil methyl esters were produced by transesterification ofMeadowfoam oil. CD₂Cl₂ was dried by distillation from CaH₂. NMR spectrawere recorded on a Varian Mercury 300 (299.817 MHz for ¹H).

Starting materials and products were characterized by comparing peakswith known standards, in conjunction with supporting data from gaschromatography retention times (GC-Agilent 6890) and mass spectrumanalysis using a mass spectrum detector (GC-MS-Agilent 5973N). Bothinstruments contained the same column and used the same method forcharacterizations: column: HP-5 30 m×0.25 mm (ID)×0.25 μm filmthickness. Manufacturer: Agilent; GC and GC-MS method conditions:

-   Injector temperature: 250° C.-   Oven temperature:-   Starting temperature: 100° C., hold time: 1 minute.-   Ramp rate 10° C./min to: 250° C., hold time: 24 minute.-   Carrier gas: Helium-   Mean gas velocity: 31.3±3.5% cm/sec (calculated).-   Split ratio: ˜50:1-   GC 6890 FID Detector

General Experimental Procedure for Examples 1-3

Substrate (0.16 mmol) and isomerization inhibitor (0.1˜1.0 equiv) weredissolved in CD₂Cl₂ (0.7 mL) in a 5 mL vial in a nitrogen-filled VacuumAtmospheres drybox (O₂<2.5 ppm). Catalyst C848 (5 mol %) was added tothe solution, and the reaction mixture was transferred to an NMR tubefitted with a screw cap. The NMR tube was taken out of the drybox, andheated to 40° C. in an oil bath. The reaction was monitored by ¹H NMR.

Example 1 Self-Metathesis Reaction of(Z)-5-t-butyldimethylsilyloxy-2-pentenoate

Product Distribution Isomerization Inhibitor 1 2 None 12% 88% 1 equiv.None None Maleic Anhydride 1 equiv. 11% 89% 2,2,2-Trifluoroethanol 1equiv. 19% 81% Nonafluoro-tert-butyl alcohol 1 equiv. 17% 83% Phenol 1equiv. >95% None Acetic Acid 10 mol % 22% 78% Tricyclohexyl phosphineoxide 10 mol % >95% None 1,4-BenzoquinoneAnalytical Information

(E)-5-tert-butyldimethylsilyloxy-2-pentenoate (1)

¹H NMR (CD₂Cl₂): δ6.96 (td, 1H, J=7.2, 15.6 Hz), 5.88 (td, 1H, J=1.5,15.6 Hz), 3.74 (t, 2H, J=6.5 Hz), 3.70 (s, 3H), 2.41 (td, 2H, J=6.5, 7.2Hz), 0.90 (s, 9H), 0.06 (s, 6H).

(Z) & (E) mixture of 5-tert-butyldimethylsilyloxy-4-pentenoate (E/Z=1:2)(2). (Ohba, T.; Ikeda, E.; Tsuchiya, N.; Nishimura, K.; Takei, H.Bioorg. Med. Chem. Lett. 1996, 6, 2629-2634.)

¹HNMR(CD₂Cl₂): δ6.30 (td, 1H, J=1.5, 12.3 Hz, E), 6.22 (dd, 1H, J=2.4,6.0 Hz, Z), 4.95 (td, 1H, 7.4, 12.0 Hz, E), 4.47 (dt, 1H, J=6.0, 7.0 Hz,Z), 2.40˜2.15 (m, 8H, E & Z), 3.65 (s, 6H, E & Z), 0.94 (s, 9H, Z), 0.92(s, 9H, E), 0.15 (s, 6H, Z), 0.13 (s, 6H, E)

Example 2 RCM Reaction of Diallyl Ether

Product Distribution Isomerization Inhibitor 3 4 None None >95% 10 mol% >95% None Acetic Acid 10 mol % >95% None 1,4-BenzoquinoneAnalytical Information

2,5 Dihydrofuran (3)

¹H NMR (CD₂Cl₂): δ5.91 (t, 2H, J=0.9 Hz), 4.60 (d, 4H, J-0.9 Hz)

2,3-Dihydrofuran (4)

¹H NMR (CD₂Cl₂): δ6.32 (m, 1H), 4.95(m, 1H), 4.28 (t, 2H, J=9.6 Hz),2.59 (m, 21H)

Example 3 Self-Metathesis Reaction of (Z)1,4-Bis(tert-butyldimethylsilyloxy)-2-butene

Product Distribution Isomerization Inhibitor 5 6 None None >95% 10 mol %None >95% Acetic acid 10 mol % >95% None 1,4-BenzoquinoneAnalytical Information

(E)-1,4-Bis(tert-butyldimethylsilyloxy)-2-butene (5)

¹H NMR (CD₂Cl₂): δ 5.77 (t, 2H, J=3.0 Hz), 4.18 (d, 4H, J=3.0 Hz), 0.92(s, 9H), 0.08 (s, 6H)

(Z) & (E) mixture of 1,4-Bis(tert-butyldimethylsilyloxy)-1-butene(E/Z=1:2.3) (6). (Kang, K.; Weber, W. P. Tetrahedron Lett. 1985, 26,5753-5754.)

¹H NMR (CD₂Cl₂): δ6.29 (td, 1H, 1.2, 12.1 Hz, E), 6.22 (td, 1H, J=1.5,5.7 Hz, Z), 4.95 (td, 1H, J=7.2, 12.1 Hz, E), 4.49 (dt, 1H, J=5.7, 7.2Hz, Z), 3.60 (t, 2H, J=6.9 Hz, Z), 3.57 (t, 2H, J=6.6 Hz, E), 2.30 (td,2H, J=6.9, 7.2 Hz, Z), 2.09 (td, 2H, J=6.6, 7.2 Hz, E), 0.94 (s, 9H, Z),0.91 (s, 9H, E), 0.15 (s, 6H, E), 0.07 (s, 6H, Z)

Example 4 Ethenolysis of 11-Eicosenyl Acetate with C823 (0.3 mol %) and1,4-Benzoquinone (0.6 mol %)

EXPERIMENTAL PROCEDURE

11-Eicosenyl acetate was degassed with anhydrous Argon for 10 minutesfollowed by adding 8 g (23.7 mmol) each into two Fisher-Porter bottles.To one bottle was added 1,4-benzoquinone (15 mg, 0.14 mmol) followed byruthenium catalyst 823 (59 mg, 0.071 mmol) at room temperature. To theother bottle was added only catalyst 823 (59 mg), as the controlreaction. Both bottles were pressured with ethylene (130 psi) andstirred for 41.5 hrs at 40° C. or room temperature. During the reaction,samples were collected and analyzed. Samples were quenched with anexcess amount of 1 M THMP solution (trishydroxymethyl phosphine in IPA)at ˜50° C. for 1 h, then analyzed by GC and GC-MS.

Ethenolysis of 11-Eicosenyl acetate Results (Reported as Percent GCArea)

11-Docosenyl Time 11-Eicosenyl 11-Dodecenyl 1,22-Diacetate,Isomerization, (min) Reaction acetate 1-Decene, 7 acetate, 89-Octadecene, 9 10 Impurities 100 Benzoquinone 42 23 32 1 2 0 Control 2728 39 2 3 1 1110 Benzoquinone 41 22 32 2 2 1 Control 23 22 32 3 4 152490 Benzoquinone 41 22 32 2 2 1 Control 23 20 28 3 4 21Analytical Information

GC and GC/MS results: Rt 2.10 min (7,1-Decene, M⁺=140), Rt 9.05 min (8,11-Dodecenyl acetate, M⁺=226), Rt 10.96 and Rt 11.03 min(9,9-Octadecene, M⁺=252), Rt 17.27 min (11-Eicosenyl acetate, M⁺=338),Rt 30.36 and Rt 31.33 min (10,11-Docosenyl 1,22-Diacetate, M⁺=424).

Example 5 Ethenolysis of Methyl Oleate, C823 (0.1 mol%)+1,4-Benzoquinone (0.2 mol %)

EXPERIMENTAL PROCEDURE

Methyl Oleate (99% pure) was degassed with anhydrous Argon for 10minutes followed by adding 12 g (40.5 mmol) each to two Fisher-Porterbottles. To one bottle was added 1,4-benzoquinone (9 mg, 0.082 mmol)followed by ruthenium catalyst C823 (33 mg, 0.041 mmol) or C712 (29 mg,0.041 mmol) at room temperature. To the other bottle was added onlycatalyst 823 (33 mg) or 712 (29 mg), as the control reaction. Bothbottles were pressured with Ethylene (160-150 psi), and stirred for 21.3hrs at 40° C. During the reaction, the reaction mixture was collected,and then quenched with excess amount of 1 M THMP solution(trishydroxymethyl phosphine in IPA) at 50° C. for 1 h and analyzed byGC and GC-MS.

Ethenolysis of Methyl Oleate Results (Reported as Percent GC Area)9-Methyl 1,18-Dimethyl Time Methyl Decenoate, 9-octadendiaoteIsomerization, (min) Reaction Oleate 1-Decene, 7 11 9-Octadecene, 8 12Impurities 100 Benzoquinone 54 23 24 1 1 <1 Control 51 21 22 1 1 <1 240Benzoquinone 53 21 23 1 1 <1 Control 33 30 31 2 2 2 360 Benzoquinone 5322 22 1 1 <1 Control 28 31 32 3 3 4 1275 Benzoquinone 53 21 23 1 1 <1Control 27 16 17 3 3 35Analytical Information

GC and GC/MS results: Rt 2.12 min (7,1-Decene, M⁺=140), Rt 5.47 min (11,Methyl 9-Decenoate, M⁺=184), Rt 10.96 and Rt 11.03 min (8,9-Octadecene,M⁺=252), Rt 14.63 min (Methyl Oleate, M⁺=296), Rt 17.66 and Rt 17.75 min(12, 1,18-Dimethyl 9-Octadecendioate, M⁺=340).

Example 6 Ethenolysis of Methyl Oleate, C712 (0.1 mol%)+1,4-Benzoquinone (0.2 mol %) EXPERIMENTAL PROCEDURE

Same as described in Example 5 except used 0.1 mol % of C712 in place ofC823.

Ethenolysis of Methyl Oleate Results (Reported as Percent GC Area)9-Methyl 1,18-Dimethyl 9- Time Decenoate, octadendiaote Isomerization,(min) Reaction Methyl Oleate 1-Decene, 7 11 9-Octadecene, 8 12Impurities 115 Benzoquinone 17 28 28 9 9 8 Control 24 17 17 12 12 17 240Benzoquinone 17 26 26 9 9 12 Control 24 17 17 12 12 17 337 Benzoquinone17 25 25 9 9 14 Control 22 18 18 11 11 19 1280 Benzoquinone 17 21 21 9 922 Control 21 11 11 11 10 35

Example 7 Ethenolysis of Meadowdoam Oil Methyl Esters, C823 (0.3 mol%)+1,4-Benzoquinone (0.6 mol %):

EXPERIMENTAL PROCEDURE

Meadowfoam oil methyl ester was degassed with anhydrous Argon for 10minutes followed by adding 10 g (31.3 mmol) to two Fisher-Porterbottles. To one bottles was added 1,4-benzoquinone (20 mg, 0.19 mmol)followed by ruthenium catalyst 823 (77 mg, 0.094 mmol) at roomtemperature. To the other bottle was added only catalyst 823 (77 mg), asthe control reaction. Both bottles were pressured with Ethylene (130psi), and stirred for 66.5 hrs at 40° C. During the reaction, thereaction mixture was collected, and then quenched with excess amount of1 M THMP solution (trishydroxymethyl phosphine in IPA) at ˜50° C. for 1h and analyzed by GC and GC-MS.

Ethenolysis of Meadowfoam Oil Methyl Ester Results (Reported as PercentGC Area) Methyl 5- Isomerization, Eicosenoate Methyl 5-hexenoate,Impurities Time (hr) Reaction 13 1-Decene, 7 16 (rt < 2.5 min) 1Benzoquinone 31 7 10 0 Control 39 6 8 0 3 Benzoquinone 30 8 11 0 Control33 7 9 <1 21.3 Benzoquinone 28 7 11 <1 Control 31 7 9 1 66.5Benzoquinone 29 7 10 <1 Control 31 4 5 9Analytical Information

GC and GC/MS results: Rt 1.67 min (16, Methyl 5-hexenoate, M⁺=128), Rt2.09 min (7,1-Decene, M⁺=140), Rt 8.88 min (1-Hexadecene, M⁺=224), Rt16.39 min (13, Methyl 5-Eicosenoate, M⁺=324), Rt 18.34 min (15, Methyl5,13-Docosadienoate, M⁺=350), Rt 18.65 min (14, Methyl 5-Docosenoate,M⁺=352).

It is to be understood that while the invention has been described inconjunction with the preferred specific embodiments thereof, theforegoing description is intended to illustrate and not limit the scopeof the invention. Other aspects, advantages, and modifications will beapparent to those skilled in the art to which the invention pertains.

All patents, patent applications, journal articles, and other referencescited herein are incorporated by reference in their entireties.

1. A method for carrying out an olefin metathesis reaction, comprisingcontacting at least one olefinic reactant with an olefin metathesiscatalyst at a temperature in the range of −72° C. to about 20° C. in thepresence of an effective amount of an isomerization inhibitor.
 2. Themethod of claim 1, wherein the olefin metathesis catalyst is atransition metal alkylidene complex.
 3. The method of claim 2, whereinthe transition metal alkylidene is a ruthenium alkylidene complex. 4.The method of claim 3, wherein the ruthenium alkylidene complex containsan N-heterocyclic carbene ligand coordinated to the ruthenium atom. 5.The method of claim 1, wherein the effective amount of the isomerizationinhibitor is effective to reduce the production of unwanted reactionproducts resulting from olefin isomerization by at least 20% relative tothe unwanted reaction products observed when the olefin metathesisreaction is carried out with no isomerization inhibitor.
 6. The methodof claim 5, wherein the effective amount of the isomerization inhibitoris effective to reduce the production of unwanted reaction productsresulting from olefin isomerization by at least 50% relative to theunwanted reaction products observed when the olefin metathesis reactionis carried out with no isomerization inhibitor.
 7. The method of claim6, wherein the effective amount of the isomerization inhibitor iseffective to reduce the production of unwanted reaction productsresulting from olefin isomerization by at least 50% relative to theunwanted reaction products observed when the olefin metathesis reactionis carried out with no isomerization inhibitor.
 8. The method of claim1, wherein two olefinic reactants are used.
 9. The method of claim 8,wherein one reactant is ethylene.
 10. The method of claim 8, wherein onereactant is an α-olefin.
 11. The method of claim 1, wherein theisomerization inhibitor is an organic acid.
 12. The method of claim 11,wherein the organic acid has a pKa in the range of 1.5 to 6.5 inclusive.13. The method of claim 12, wherein the organic acid has a pKa in therange of 3.0 to 4.8 inclusive.
 14. The method of claim 11, wherein theorganic acid has a molecular weight of at most 250 g/mole.
 15. Themethod of claim 14, wherein the organic acid has a molecular weight ofat most 175 g/mole.
 16. The method of claim 11, wherein the organic acidhas the formula R¹⁰—COOH where R¹⁰ is selected from H, C₁-C₆ alkyl,C₂-C₆ alkenyl, halogenated C₁-C₆ alkyl, halogenated C₁-C₆ alkenyl,phenyl, halogenated phenyl, benzyl, and halogenated benzyl.
 17. A methodfor carrying out an ethenolysis reaction, comprising contacting ethyleneand at least one additional olefinic reactant with an olefin metathesiscatalyst at a temperature in the range of −72° C. to about 20° C. in thepresence of a quinone, a substituted quinone, BHT, vitamin E, and/or anorganic acid having the formula R¹⁰—COOH where R¹⁰ is selected from H,C₁-C₆ alkyl, C₂-C₆ alkenyl, halogenated C₁-C₆ alkyl, halogenated C₁-C₆alkenyl, phenyl, halogenated phenyl, benzyl, and halogenated benzyl,wherein the organic acid is present in an amount effective to inhibitolefin isomerization.
 18. A method for carrying out an olefin metathesisreaction, comprising contacting an α-olefin and at least one additionalolefinic reactant with an olefin metathesis catalyst at a temperature inthe range of −72° C. to about 20° C. in the presence of a quinone, asubstituted quinone, BHT, vitamin E, and/or an organic acid having theformula R¹⁰—COOH where R¹⁰ is selected from H, C₁-C₆ alkyl, C₂-C₆alkenyl, halogenated C₁-C₆ alkyl, halogenated C₁-C₆ alkenyl, phenyl,halogenated phenyl, benzyl, and halogenated benzyl, wherein the organicacid is present in an amount effective to inhibit olefin isomerization.19. An olefin metathesis reaction system, comprising ethylene, a secondolefinic reactant, an olefin metathesis catalyst, an isomerizationinhibitor acid, and, if an olefin metathesis reaction has begun, atleast one ethenolysis product.
 20. An olefin metathesis system,comprising an α-olefin, a second olefinic reactant, an olefin metathesiscatalyst, an isomerization inhibitor selected from H, C₁-C₆ alkyl, C₂-C₆alkenyl, halogenated C₁-C₆ alkyl, halogenated C₁-C₆ alkenyl, phenyl,halogenated phenyl, benzyl, and halogenated benzyl, and if an olefinmetathesis reaction has begun, at least one olefin metathesis product.